Is there a way for non-root processes to bind to “privileged” ports on Linux?

Question

It\'s very annoying to have this limitation on my development box, when there won\'t ever be any users other than me.

I\'m aware of the standard workarounds, but non

Answer 1

I tried the iptables PREROUTING REDIRECT method. In older kernels it seems this type of rule wasn't supported for IPv6. But apparently it is now supported in ip6tables v1.4.18 and Linux kernel v3.8.

I also found that PREROUTING REDIRECT doesn't work for connections initiated within the machine. To work for conections from the local machine, add an OUTPUT rule also — see iptables port redirect not working for localhost. E.g. something like:

iptables -t nat -I OUTPUT -o lo -p tcp --dport 80 -j REDIRECT --to-port 8080

I also found that PREROUTING REDIRECT also affects forwarded packets. That is, if the machine is also forwarding packets between interfaces (e.g. if it's acting as a Wi-Fi access point connected to an Ethernet network), then the iptables rule will also catch connected clients' connections to Internet destinations, and redirect them to the machine. That's not what I wanted—I only wanted to redirect connections that were directed to the machine itself. I found I can make it only affect packets addressed to the box, by adding -m addrtype --dst-type LOCAL. E.g. something like:

iptables -A PREROUTING -t nat -p tcp --dport 80 -m addrtype --dst-type LOCAL -j REDIRECT --to-port 8080

One other possibility is to use TCP port forwarding. E.g. using socat:

socat TCP4-LISTEN:www,reuseaddr,fork TCP4:localhost:8080

However one disadvantage with that method is, the application that is listening on port 8080 then doesn't know the source address of incoming connections (e.g. for logging or other identification purposes).